As a defense system for ships, basic point facilities and the like, a free electron laser (FEL) apparatus has been proposed. The FEL apparatus can destroy a target by collectively irradiating energy to one point in a space by the free electron laser and inactivate an offensive weapon.
FIG. 1 is a diagram showing a configuration example of an FEL apparatus 500 that uses a typical RF accelerator. With reference to FIG. 1, the FEL apparatus 500 contains a microwave source 51, a pulse compressor 52, a waveguide 53, a coupler 54, an electron gun 55, a plurality of accelerators 56-1 and 56-2, a damper 57, an undulator 58 and reflection mirrors 59.
The microwave (RF power) generated by the microwave source 51 is pulse-compressed by the pulse compressor 52 and then supplied through the waveguide 53 and the coupler 54 to each of the accelerators 56-1 and 56-2. The free electrons generated by the electron gun 55 are accelerated close to a light speed by the accelerators 56-1 and 56-2. When the free electrons are passed through the undulator 58, radiation light is generated. Since the radiation light generated through the undulator 58 travels back and forth between the reflection mirrors 59, coherency is improved, and the radiation light is outputted as laser light 600 with a wavelength depending on the energy of the free electrons and the undulator period. It should be noted that the remaining electric power after the electric power is used to accelerate the free electrons is converted into thermal energy in dummy loads 60-1 and 60-2.
Also, Japanese Patent No. 4,066,330 discloses a radiation light generating apparatus that has an energy recovery type pre-accelerator which can be operated in a small RF power (refer to Patent Literature 1). In the radiation light generating apparatus disclosed in Patent Literature 1, the energy recovery type pre-accelerator is arranged on a circular trajectory, and a resonant frequency of an acceleration cavity of the pre-accelerator is slightly detuned from a frequency of the RF power to be used, recover the energy of electron beam. This technique can be applied to the FEL apparatus. Typically, these radiation light generating apparatuses use the RF source for only the acceleration or deceleration of electrons of the beam (electrically charged particles) irrespectively of the electron beam energy recovery.
The free electron laser has a property of going straight and can capture a target in the light speed. Thus, without requiring a conventional ballistic calculation and inducing apparatus by considering external disturbance such as a weather condition, it is possible to increase a hitting precision to a flying object that moves at a high speed. However, when the flying object passes through a region which has influence on a refraction index of the laser light, such as a rain, snow, fog, cloud, or a great temperature difference, the energy density of the laser light is attenuated. Thus, there is a fear that the desirable result cannot be obtained.